This invention relates to a belt press for increasing the solids concentration of a slurry by reducing the liquid component.
Belt presses have been known for many years and have been used in many applications, such as the dewatering of sewage sludge, peat, industrial wastes, cement slurries, and coal slurries. The belt press of the present invention was designed to handle large volumes of slurry containing a wide variety of solids, including coarse, abrasive, relatively incompressible materials as well as fines, such as occur in coal tailings slurry, but could be used in other applications as well.
One application in which a belt press is particularly suitable is for dewatering of coal tailings. Coal tailings are the materials that are washed from coal after it has been crushed. The wash water from the coal washing operation is pumped into a thickener, such as a large cylindrical tank, where the solids settle to the bottom and the clear water flows out of a top launder for reuse in the coal washer. The settled material is collected at the bottom and is pumped out of the thickener. This material, known as the thickener underflow, typically contains about 60-80% water and about 20-40% solids. The solids include minerals such as rock, chemically undesirable materials such as pyrites, and fines such as clay, silt and coal fines. In the past, the underflow has been pumped into settlement ponds with the purpose of allowing the water to percolate down into the ground. In practice, this has not been a satisfactory method of disposal because the fines in the tailings sink to the bottom and form an impervious blanket that retains the water in the pond. Since the ponds remain fluid for years, the land usage of this procedure is excessive. If the tailing slurry could be dewatered prior to disposal, it could be handled and used like dirt for strip mine backfill and other useful purposes. Effective dewatering of the tailing slurry would convert this material from a problem to an asset.
Belt presses in the past have encountered many problems, and the present invention is intended to remedy many of those problems. For example, other presses have encountered problems in their belt tensioning systems. The belt tensioning systems are typically controlled by two air or hydraulic cylinders, air bags, diaphragms, or other fluid actuators which are attached to pistons, which in turn support a belt tensioning roll. The pistons in those fluid actuators must move together, otherwise the belt tensioning roll becomes skewed relative to the belt which causes unnecessary wear on the belt and causes the belt to track incorrectly. Therefore, many manufacturers have provided various schemes to ensure that the two pistons move together. For example, U.S. Pat. No. 1,347,121 "Rice" describes a rack and pinion structure mounted on the belt press frame for preventing skewing of the belt tensioning roll. However a rack and pinion system is quite expensive and difficult to adjust, and the rack and pinion may become jammed if the slurry overflows the belt and gets into the rack teeth. The present invention provides, a simple, inexpensive, easily adjustable cable arrangement for keeping the belt tensioning roll aligned.
Another problem encountered in belt tensioning systems of the prior art is that belts may become greatly elongated by stretching before wearing out, but the fluid actuators of the known belt tensioning systems are not able to extend as far as the belt stretches. Consequently, the belts must be replaced before they are actually worn out, which is quite an expensive and time consuming undertaking. The present invention solves this problem by providing an extension adjustment on the primary belt tensioner, and by providing a secondary belt take-up adjustment.
Belt tracking systems which are intended to keep the belt running in a straight line are known in the art. The belt tracking systems typically include a sensor for determining when the belt is deviating from center, a steering roll which can be skewed relative to the line of travel of the belt in order to steer the belt back into the proper alignment, and a roll steering mechanism for controlling the angle of the steering roll. In belt tracking systems of the prior art, the rolls are typically mounted on bearings which can tip or be deflected upward or downward. These undesired bearing motions may misalign and prematurely wear out the bearing or unduly stretch the belt. It also reduces the tracking effect of the roll which necessitates increased steering motion and further exacerbates the wear problem. The present invention includes a roll mounting system which overcomes these problems.
Some belt presses of the prior art include inclined wedge sections for preliminary dewatering of the slurry. These wedge systems are typically very difficult to adjust and do not include enough types of adjustment to enable them to optimally handle a variety of slurries. The present invention provides a wedge section which is easy to adjust and which adjusts in several different directions so as to provide optimum dewatering.
The drain systems in prior art belt presses increases the width of the press so that they may need disassembly for shipment. The width also increases the effective area which the belt press occupies and may constitute a safety hazard to people working around the machine. This invention provides an internal drain system that can accommodate large volumes of liquid from slurries, yet is easily accessible for cleaning or service.
In belt presses of the prior art, replacement of the belts has always required substantial time for disassembly of the press. The present invention provides simple means for replacing belts, from either side of the press, in a brief time period.